Linear constant current LED drive device capable of driving reduced number of LEDs

Abstract

A linear constant current LED drive device capable of driving reduced number of LEDs, comprises: a rectifier module, an energy storage component, a switch module, a constant current supply module, a measurement module and a control module. When voltage differences between two ends of both switch module and constant current supply module are less than according threshold voltages, control module turns on switch module, enabling rectifier module to charge energy storage component and LED string lights. When voltage difference between two ends of either switch module or constant current supply module exceeds according threshold voltage, control module turns off switch module, enabling energy storage component to charge LED string lights. So rectifier module and energy storage component supply electricity to plurality of LED string lights alternately, number of LEDs can be reduced, while maintaining high drive efficiency.

What is claimed is: 
     
       1. A linear constant current LED drive device capable of driving reduced number of LEDs, wherein comprises a rectifier module, an energy storage component, a switch module, a constant current supply module, a measurement module and a control module;
 the rectifier module rectifies an alternating current (AC) from an external input, and supplies power to both the energy storage component and a plurality of LED string lights; the switch module controls the energy storage component to charge and discharge and a power supply to the plurality of LED string lights through an on-off of the switch module; the constant current supply module keeps the current of the plurality of LED string lights constant; the measurement module measures a voltage difference between two ends of the constant current supply module before outputting the voltage difference measured to the control module; when the voltage difference between two ends of the switch module is less than a first threshold voltage, and the voltage difference between two ends of the constant current supply module is less than a second threshold voltage, the switch module will be controlled on, so as to enable the rectifier module to charge the energy storage component and supply power to the plurality of LED string lights; when the voltage difference between two ends of the switch module exceeds the first threshold voltage, or the voltage difference between two ends of the constant current supply module exceeds the second threshold voltage, the switch module is controlled off so as to enable the energy storage component to supply power to the plurality of LED string lights. 
 
     
     
       2. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 1 , wherein the first threshold voltage is a highest voltage it may afford between two ends thereof, when the switch module is turned on. 
     
     
       3. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 1 , wherein the control module comprises:
 a level shift unit, applied to shifting a level of the voltage output by the measurement module, so that the voltage output from the measurement module is shifted to a voltage domain of the switch module; 
 a switch voltage measurement unit, applied to measuring the voltage difference between two ends of the switch module, and comparing the voltage difference between two ends of the switch module to the first threshold voltage; 
 a switch control unit, applied to controlling the switch module on so as to charge the energy storage component, when the voltage difference between two ends of the switch module is less than the first threshold voltage, and the voltage difference between two ends of the constant current supply module is less than the second threshold voltage; while controlling the switch module off so as to stop charging the energy storage component, when the voltage difference between two ends of the switch module exceeds the first threshold voltage, or the voltage difference between two ends of the constant current supply module exceeds the second threshold voltage. 
 
     
     
       4. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 3 , wherein the drive device further comprises a unidirectional conduction module, applied to a forward direction conduction to preventing a leakage of the energy storage component; the switch module connects to one end of the energy storage component and a positive electrode of the plurality of LED string lights through the unidirectional conduction module. 
     
     
       5. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 4 , wherein the switch module comprises a first MOS transistor, a drain electrode of the first MOS transistor connects to an output end of the rectifier module, a source electrode of the first MOS transistor connects to a positive electrode of the unidirectional conduction module, a gate electrode of the first MOS transistor is an input end for a control signal of the switch module, connecting to the switch control unit. 
     
     
       6. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 5 , wherein the level shift unit comprises a power supply, a first resistor and an inverter; a negative electrode of the power supply gets grounded, a positive electrode of the power supply connects to one end of the first resistor and a positive end of a power supply of the inverter, another end of the first resistor is an input end of the level shift unit, connecting to an output end of the measurement module and an input end of the inverter, a negative end of the power supply of the inverter gets grounded, and an output end of the inverter is an output end of the level shift unit, connecting to the gate electrode of the first MOS transistor. 
     
     
       7. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 3 , wherein the measurement module comprises a second resistor, a third resistor, a first reference voltage source, a second MOS transistor and a comparator; one end of the second resistor is an input end of the measurement module, connecting to an input end of the constant current supply module and a negative electrode of the plurality of LED string lights, another end of the second resistor connects to an non-inverting input end of the comparator, and further gets grounded through the third resistor; a positive electrode of the first reference voltage source connects to an inverting input end of the comparator, a negative electrode of the first reference voltage source gets grounded, an output end of the comparator connects to a gate electrode of the second MOS transistor, while a source electrode of the second MOS transistor gets grounded, and a drain electrode of the second MOS transistor is an output end of the measurement module, connecting to the switch control unit. 
     
     
       8. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 7 , wherein the constant current supply module comprises a fourth resistor, a second reference voltage source, a third MOS transistor and an operational amplifier; a drain electrode of the third MOS transistor is the input end of the constant current supply module, connecting to a negative electrode of the plurality of LED string lights outside and one end of the second resistor, a source electrode of the third MOS transistor is connected to an inverting input end of the operational amplifier and gets grounded through the fourth resistor, a positive electrode of the second reference voltage source is connected to an non-inverting input end of the operational amplifier, while a negative electrode of the second reference voltage source gets grounded. 
     
     
       9. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 1 , wherein the energy storage component comprises a capacitor. 
     
     
       10. The linear constant current LED drive device capable of driving reduced number of LEDs according to  claim 4 , wherein the unidirectional conduction module includes a diode, the switch module connects to one end of the energy storage component and the positive electrode of the plurality of LED string lights through the diode.